Phase 6: add PI_AUTO_COMPACT_FOLLOW_UP_PREFIXES — document pi-auto-compact phrases.

Constants match SPEC §16.9 for tests and docs; runtime v1 does not match follow-up text.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/auto-compact.test.ts

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+import { describe, expect, it } from "vitest";
+import {
+	detectAndCachePiAutoCompact,
+	detectPiAutoCompact,
+	PI_AUTO_COMPACT_FOLLOW_UP_PREFIXES,
+	resolveDeliveryMode,
+} from "../src/auto-compact";
+import { createDefaultSettings } from "../src/settings";
+import { createRuntimeFlags } from "../src/state";
+
+describe("detectPiAutoCompact", () => {
+	it("returns true when auto-compact command is registered", () => {
+		const pi = {
+			getCommands: () => [{ name: "auto-compact" }],
+		};
+		expect(detectPiAutoCompact(pi as never)).toBe(true);
+	});
+
+	it("returns false when auto-compact command is absent", () => {
+		const pi = {
+			getCommands: () => [{ name: "skill-reinject" }],
+		};
+		expect(detectPiAutoCompact(pi as never)).toBe(false);
+	});
+});
+
+describe("detectAndCachePiAutoCompact", () => {
+	it("writes detect result into runtime flags", () => {
+		const runtime = createRuntimeFlags();
+		const pi = {
+			getCommands: () => [{ name: "auto-compact" }],
+		};
+		expect(detectAndCachePiAutoCompact(pi as never, runtime)).toBe(true);
+		expect(runtime.autoCompactDetected).toBe(true);
+	});
+});
+
+describe("resolveDeliveryMode", () => {
+	it("defers when pi-auto-compact is cached as detected", () => {
+		const runtime = createRuntimeFlags();
+		runtime.autoCompactDetected = true;
+		expect(resolveDeliveryMode(createDefaultSettings(), runtime)).toBe("defer");
+	});
+});
+
+describe("PI_AUTO_COMPACT_FOLLOW_UP_PREFIXES", () => {
+	it("documents pi-auto-compact follow-up phrases from SPEC §16.9", () => {
+		expect([...PI_AUTO_COMPACT_FOLLOW_UP_PREFIXES]).toEqual([
+			"Auto-compact ran before this turn.",
+			"Auto-compact ran mid-turn.",
+			"Emergency auto-compact ran.",
+			"Auto-compact ran on session resume.",
+		]);
+	});
+});